Cross flow filtration systems separate a liquid or gas fluid mixture into two component fluids. There are multiple applications for cross flow filtration systems throughout most industries, including the purification of parts washing baths, removal of dyes from waste streams, concentration of sap for more efficient production of maple syrup, separation of fermentation products from a brew, and purification of salt water to produce fresh drinking water. This invention is specifically applicable to any liquid or gas fluids in microfiltration, ultrafiltration, nanofiltration and reverse osmosis applications.
Filters are a porous mass through which a gas or liquid is passed to separate matter in suspension. Frequently membranes are attached to a filter media to establish a semipermeable barrier that selectively rejects some solutes while passing others. Membranes can also separate solute without the use of a filter substrate. In the following discussion the term filter includes membranes. Filters are made of polymers, ceramic, stainless steel, and other materials including liquids.
Pressure and flow are used to deliver a fluid to the filter surface. Cross flow filters have a component of the total flow along the filter surface. Flow along the filter surface helps keep the filter clean. Flow along the surface of the filter can be recycled. In this invention and in U.S. Pat. No. 5,725,758 recycled flow, which may or may not pass through the filter, is used to suck feedstock into the recirculation loop.
That portion of the fluid mixture which is forced through the filter is referred to as permeate. The permeate is a purified fluid mixture. The remaining portion of the fluid in the filtration system which does not pass through the filter is referred to as retentate. The retentate is the residual fluid mixture. The retentate contains molecules and particles too large to pass through the filter. Once removed from the filtration system, the retentate becomes known as concentrate. Feedstock, which is the fluid to be subject to filtration, is forced or, in this invention, sucked into the retentate to replace the permeate.
Batch filtration systems pump a feedstock under pressure to a cross flow filter. The permeate which flows through the filter is collected as permeate. The retentate that remains in the system downstream from the filter is expelled as concentrate after a single pass through the cross flow filter. Continuous filtration systems use a feed pump to add under pressure a feedstock to the retentate. The retentate is continually recycled under pressure with a recirculation pump in a closed loop. Concentrate is removed from the filtration system after passing the cross flow filter several times (on average). When removed, the concentrate is at a desired concentration of the desired component. This invention primarily applies to continuous filtration using a single pump, although one example is presented and claimed for batch filtration.
An invention defined herein as a CHUF is frequently mentioned in the following text. The CHUF best fits the definition of valve. A valve is defined as any of numerous mechanical devices by which the flow of liquid or gas may be started, stopped, or regulated by a movable part that opens, shuts, or regulates one or more ports or passageways.
The CHUF is a rather enhanced valve since it combines into a single structure a venturi and a bypass flow control valve. In further embodiments the CHUF also comprises, two flow control valves, temperature sensor, pressure sensors, and a flow sensor. The CHUF is made of plastic, stainless steel, or other material. It greatly simplifies the construction and control of continuous filtration systems.
The CHUF contains a venturi which sucks feedstock into the filtration system. A venturi is a short tube that is inserted in a pipeline, that has flailed ends connected by a restricted middle, that depends for operation upon the fact that as the velocity of the flow of a fluid increases in the constricted part, the pressure decreases, and that is used for producing suction. Aspirators produce suction, and eductors extract. The term aspirators or eductors are equivalent to the term venturi if suction or extraction depends upon the flow of a fluid or pressure of a flowing fluid.
Most of the referenced patents refer to the sucking of a fluid into a system. Referenced U.S. Pat. No. 5,725,758 by Chace et al., U.S. Pat. No. 4,026,800 by Friedrick et al. and U.S. Pat. No. 5,395,514 by Siegler are most closely related to this invention. Fredrick's patent discloses combining a sucking means before a pump and bypassing part of the fluid to be entered to the orifice, by means of a valve, and directing the fluid not passed to the orifice to the pump. In Fredrick's patent the bypass connects to the suction side of the venturi. Unlike Fredrick's patent the bypass in this invention and in U.S. Pat. No. 5,725,758 is completely around the venturi. The bypass described in Fredrick's patent is different from that in this invention as they serve different purposes.
Siegler discloses a membrane filtration apparatus that uses a sucking device and flow control valve. Siegler removes concentrate from the filtration system through a diverter. This concentrate is then mixed in a container with the existing feedstock and sucked back into the filtration system through the suction side of a venturi (eductor). In this invention the bypass is again completely around the venturi. Also, in this invention concentrate is removed only when it is totally concentrated, and never recycled back through the system as a component of feedstock as does Siegler's invention.
The inventions by Seigler, Fredrick, and Chace all use a control valve to control sucking of a feedstock fluid into a system. However, what must be evaluated is the effect of the control valve on the entire, closed loop system--not just on the control of suction. In addition to sucking fluid into the filtration system, the control valve in this invention and the control valve in the patent by Chace also control pressure within a closed loop. Pressure at the filter determines the rate of permeate production (flux). Therefore, in this invention a single control valve simultaneously controls inflow of feedstock into the filtration system through the venturi, which is flow dependent, and outflow through the filter, which is pressure dependent. No other referenced patent achieves this goal.